The present invention relates generally to test equipment, and more specifically to a test device for a wrench.
Threaded fasteners are tightened by a wide variety of tools and control techniques. To ensure quality of fastened joints, an inspection may be performed periodically to ensure that the tools used to perform the tightening continue to apply the correct torque. This xe2x80x9cauditxe2x80x9d is typically performed on pre-tightened joints using dial wrenches, indicator wrenches and electronic wrenches to check the torque required to rotate a fastener by a small amount. The torque read from the wrench is related to the initial tightened torque.
A number of factors may introduce variance into the torque readings. These may include, for example, variations in friction, the accuracy of the current torque reading, the original torque prior to the current reading, and operator error. These sources of variance may introduce so much scatter in the actual torque values that the performance of the tool is obscured. It is desirable to establish a test technique to determine which audit method and tool provides the best performance.
U.S. Pat. No. 4,244,213 and 4,319,494 are incorporated by reference herein in their entireties, for their teachings on measurement of torque previously applied to fasteners.
U.S. Pat. No. 4,150,559 and 5,886,246 describe test devices for tools. These test devices simulate joint conditions, but do not simulate pre-tightened joints.
Optimally, a repeatability and reproducibility test is conducted. In testing the tool, it is desirable to present multiple appraisers with the same test condition, so that the effect of operator influence on the test results can be measured. Unfortunately, it is difficult to exactly duplicate the condition of a threaded joint because each time a joint is disturbed, the friction conditions change.
A test apparatus is desired that can reliably repeat a given test condition, and is adjustable to simulate a variety of joint conditions, joint stiffnesses, degrees of stick-slip, and breakaway torque.
A test device includes a torque sensor that outputs an indication of torque when rotated by a tool to be tested. A rotatable arm is connected to the torque sensor. A stop prevents the arm from rotating past a rest position. At least one of the group consisting of the arm and the stop includes a magnet. The magnet causes a magnetic force that attracts the arm toward the rest position when the arm is at or near the rest position. At least one elastic member urges the arm toward the rest position. A piston optionally forces the tool to apply a torque at an adjustable repeatable application speed.